The utilization of silver halide technology in the Graphic Arts Industry has been primarily focused on the creation of high contrast systems, which are necessary to obtain strong discrimination of image and good image quality-dot characteristics. To this end, the earliest high contrast system, which is called the "lith" system, utilized a low sulfite, hydroquinone based developer with silver chlorobromide emulsions, further modified by polyethyleneoxide compounds.
The "lith" system provided high contrast, excellent image discrimination and good "dot" characteristics. The single greatest drawback of the system was the instability of the developer system which required a multi-part, compound developer and a low temperature (75.degree.-80.degree. F.) processing solution in order to maintain controlled developing solutions. These conditions further necessitated long processing times, sometimes as much as 21/2 minutes for development, but more commonly 11/2 minutes. The process was further complicated by the fact that "non-lith" films were frequently also processed in the same developers due to convenient configurations at various customers.
In order to increase development rates and lower processing times, the Graphic Arts Industry gravitated to the use of auxiliary developing agents in addition to hydroquinone. These agents include metol, phenidone, and the like. Simultaneously, to increase developer life, the developing solutions employed higher concentrations of sulfite to extend the lifetimes of the solutions, increase their resistance to aerial oxidation, afford greater uniformity of developer condition, and allow an increase in development rate by increasing the temperature of the processing solution. These new "rapid access" developers were simpler to maintain, dilutable, and required about 30 seconds of development time, affording faster throughput, ease of operation, and greater compatibility with non-lith type films. The single greatest drawback of these systems was the lack of the excellent image discrimination and dot characteristics that had been achieved with the lith system.
In U.S. Pat. No. 3,730,727, the use of formyl phenylhydrazines incorporated in the developer is discussed to improve image discrimination without the use of the low-sulfite lith techniques. It was shortly brought to practice in the "lith" system described in U.S. Pat. No. 4,224,401, which describes a lith-type result with a high pH, high sulfite-type developer solution. In U.S. Pat. No. 4,269,929, the system is further refined by employing alkanol amines to lower the operable pH of the developer to practical levels, thus permitting commercialization of the type of developer known as "hybrid" developer. Hybrid developers provide the results of lith developers but at rapid access developing speeds.
Subsequent to the foregoing disclosures, U.S. Pat. Nos. 4,686,167, 4,798,780, 4,937,160, and 4,882,261, all disclosed novel hydrazine "nucleators" which afforded the hybrid effect.
While hybrid systems have been commercialized, the flaw of the hybrid system resides in the alkanol amines incorporated within the developer solution to boost or promote high contrast. These amines, which still required a pH of 11.0 or greater, had the adverse effects of attacking the processor equipment and were basically incompatible with a great variety of non-hybrid lithographic films that were frequently processed in the same chemistries.
An approach to overcome the flaws of developer solutions containing alkanol amine was disclosed in U.S. Pat. Nos. 4,975,354 and 4,994,365. These patents taught a new hybrid system which removed the alkanol amines from the developer and positioned them in the film. These amines, ostensibly called boosters, were to activate the film incorporating the hydrazine nucleators, thus making them compatible with standard, low cost developing solutions.
The drawback of the systems which incorporated the alkanol amine boosters into the film containing the nucleators was the complexity of balancing the nucleator with the boosters to provide good discrimination at low fog or pepper levels while broadening the degree of compatibility with a number of existing rapid access developer systems.
To this end, U.S. Pat. No. 4,994,354 described the use of alkyl substituted, quaternary pyridine nucleators and U.S. Pat. No. 4,988,604 described the use of aryl sulfonamidophenyl hydrazide nucleators containing both thio and ethyleneoxide groups which were compatible with boosters and afforded good discrimination and good dot characteristics. The drawback of this system is the interaction of the nucleator and booster. That interaction limits the system's compatibility with many existing rapid access systems.
It is an object of the present invention to provide nucleator compounds having contrast enhancing properties superior to those in the prior art in conjunction with high dot quality and speed so that photographic film can be produced without a need for incorporating nucleation boosters in the formulation.
It is another object of the invention to produce superior nucleator compounds that incorporate isothiouronium salts in the formulae or structures of the compounds.
Yet another object of the invention is to provide photographic film elements that produce a high contrast image without requiring the use of nucleator boosters by incorporating nucleators in the film comprising isothiouronium substituted sulfonamidophenyl hydrazides.
A further object of the invention is to provide a process for forming a high contrast image by employing novel nucleators comprising isothiouronium substituted sulfonamidophenyl hydrazides.